Inclinometer



S p 7, 1955 K. o. HEINTZ ETAL INCLINOMETER 2 Sheets-Sheet 1 Filed Dec.31, 1953 INVENTORS. James H. Dunaway. BY Allen ,4- Chernosky,

Kar/ 0- He/nfz,

FIG. 5B.

p 27, 1955 K. o. HElNTZ ET AL INCLINOMETER 2 sheets-Sheet 2 Filed Dec.31, 1955 United States Patent warmer rerun Karl O. Heintz, James H.Dunaway, and Allen A.

Chernoslry, Houston, Tex, assignors, by mesne assignments, to EssaResearch and Engineering Company, Elizabeth, N. 5., a corporation ofDelaware Application December 31, 1353, Serial No. 401,510

8 Claims. (Cl. 33215) The present invention relates to new and improvedapparatus for determining the extent of inclination of an object from avertical position. More particularly, the invention relates to improvedapparatus for determining at the surface of the earth the inclination ofa well logging instrument or similar device while it is in a well borein the earth at any desired depth. I

In the drilling of oil wells, particularly when employing present dayconventional rotary drilling methods, it is often difiicult if notimpossible to cause the drill always to progress vertically downward atgreat depths into the earth. Also in conventional drilling practice, itsometimes becomes desirable to divert the drill purposefully away from avertical direction. In either case it becomes desirable frequently tomeasure the direction and amount of inclination of the well bore fromthe vertical throughout its length so that the position of the bottom ofthe well, or of any intermediate portion of the well bore, relative tothe mouth of the well may be calculated with reasonable accuracy. Tothis end, many forms of apparatus and combinations of apparatus elementshave been devised to yield the desired information.

It is one object of the present invention to provide an improvedapparatus for determining inclination from the vertical. It is anotherobject of the present invention to provide an improved apparatus whichmay be used in combination with orientation devices to determine boththe direction and amount by which a well bore or a device in the wellbore deviates from the vertical. It is a further object of the inventionto provide an apparatus which will record this information as the wellbore is traversed by the apparatus.

Stated briefly, the apparatus of the present invention comprises a freependulum, and a smaller, yieldably restrained pendulum which is carriedupon the free pendulum. When the apparatus is supported with its centralaxis in a vertical position, the free pendulum is free to rotate aroundthis central axis carrying the entire restrained pendulum with it. Inthe aforementioned vertical position, the pendulum arm of the restrainedpendulum is also movable around a vertical axis but the restrainingelement associated with this smaller pendulum causes the small pendulumarm to take up a predetermined position arcuately spaced around thecentral axis from the center of gravity of the free pendulum. When thecentral axis of the apparatus is tilted from the vertical position, thecenter of gravity of the free pendulum moves into a position below thetilted central axis and the restrained pendulum arm moves arcuately,relative to the center of gravity of the free pendulum, from theaforementioned predetermined position toward the direction of tilt ofthe central axis.

A preferred embodiment of the apparatus of the present invention alsocomprises at least two mirrored surfaces associated, respectively, withthe free pendulum and with the restrained pendulum, a light sourceadapted to revolve around the central axis of the apparatus,

2,718,707 Patented Sept. 27, 1955 ice a photosensitive cell adapted torevolve in fixed relation to the light source and so positioned as toreceive reflected light from each of the mirrored surfaces during someportion of each revolution around the central axis, and means forrevolving the light source and photosensitive cell around the centralaxis at a uniform rate.

The nature and objects of the invention can be more fully understoodfrom the ensuing description when considered in conjunction with theaccompanying drawings in which:

Figure 1 is an elevation view, partly in section, of one embodiment ofapparatus employing the present invention;

Figure 2 is a sectional view along the line IIII of Figure 1;

Figure 3 is a sectional view along the line IIIIII of Figure 1;

Figure 4 is a sectional view along the line IVIV of Figure 1;

Figures 5A and 5B represent the type of records produced by recordingelements employed with the apparatus of the present invention;

Figure 6 is an elevation view, partly in section of another embodimentof apparatus employing the present invention;

Figure 7 is a plan view of the apparatus of Figure 6;

Figure 8 is an elevation view, partly in section, of a preferredembodiment of apparatus employing the pres ent invention; and

Figure 9 is a sectional view along the line IXIX of Figure 8.

In the following description of the several figures of the drawing, itis assumed, for purposes of simplification of description anddefinition, that the apparatus, as described, is held or supported withits principal central axis in a vertical position. It will beappreciated, however, that in normal operation this principal centralaxis may be tilted away from vertical whereupon certain elements of theapparatus will move relative to this central axis.

Referring first to Figures 1 and 2, the apparatus of this invention maybe suitably enclosed within a housing 10 which will generally becylindrical although it may, of course, be of any other desired shape.Within the housing 10 are a pair of conventional ball or roller bearings11 Whose outer race members may be secured against movement with respectto housing 10 by any appropriate means, such as the set screws 12.Fitted concentrically Within the inner race members of bearings 11 is anelongated, usually cylindrical, support member 13 whose centrallongitudinal axis 14 is preferably coaxial with respect to the centralaxis of housing 10. For purposes of the present description, it will beassumed that both of the aforementioned axes are coaxial and may bereferred to indiscriminately by the reference numeral 14. The lower endof support member 13 may be provided with a plate, or equivalentelement, 15 adapted to bear against a suitable thrust bearing, such asthe ball thrust bearing 16, carried on plate 17 within housing 10.

Affixed to one side of support member 13 is a major mass 18. The size,shape, and placement of mass 18 upon support member 13 will depend to alarge extent upon the mass symmetry of support member 13 and upon thedistribution of other masses which may be mounted upon member 13. Sincethe primary purpose of mass 18, when combined with support member 13, isto form a free pendulum adapted to rotate freely around axis 14, it willbe appreciated that the size, shape, and placement thereof should bechosen so that the effective center of gravity of these elements isadjacent the point CG in Figures 1 and 2. Hereinafter and in theappended claims, this effective center of gravity will be referredtogenerally as the center of gravity of the major mass 18. From theforegoing, it will be appreciated that although the mass 18 has beenshown exterior of the support member 13, the mass may, if desired, bemounted on the interior of the support member so long as the effectivecenter of gravity thereof is eccentric (i. e. spaced radially) withrespect to central axis 14.

It will be apparent to workers in the art that, when the central axis 14is vertical, the support member 13 carrying mass 18 is free to rotatearound axis 14. However, when the apparatus is tilted so that, forexample, the upper end of axis 14 is tilted to the left within the planerepresented by the surface of the paper on which Figure 1 is drawn, mass18 will rotate around axis 14 until its center of gravity is in the sameplane as axis 14 and in the direction of tilt of said axis. In otherwords, with the as sumed direction of tilt mentioned above, mass 18would move arcuately through 180 degrees from the position shown in thedrawing. Movement of mass 18 would, of course, cause support member 13to turn about its central axis.

Carried upon the upper end of support member 13 by a plate, orequivalent supporting structure, 19 is a restrained pendulum or Weightedarm assembly comprising a minor mass 20 affixed to the outer extremityof a lever arm 21. The weight of minor mass 26 is but a small fractionof the weight of mass 18 and need be only large enough to impart aturning moment to lever arm 21. As may be seen from Figure 1, the innerextremity of lever arm 21 is secured to a vertical shaft 22 so that arm21 is held in a horizontal position when axis 14 and shaft 22 arevertical. In other words, the lever arm 21 is arranged in a plane whichis substantially perpendicular to the axis of the shaft 22. Shaft 22 ismounted for substantially frictionless rotation on jeweled pivotbearings 23 and 24, or the equivalent. Pivot bearings 23 and 24 are, inturn, held in place relative to plate 19 by brackets 25 and 26respectively. Resilient spring means, such as a flat spiral hair spring27 encircling shaft 22, is anchored at its outer end to bracket 25 andthence through plate 19 to support member 13. The inner end of spiralspring 27 is operatively connected to lever arm 21 by direct attachmentto shaft 22 on which lever arm 21 is secured.

It will be appreciated that spring 27 may be so adjusted that, whenshaft 22 is vertical, arm 21 and mass 20 will always come to the restingor reference position represented by the solid-line outline of theseelements in Figure 3. On the other hand, when the upper end of shaft 22is tilted to the right in the plane of the paper on which Figure 1 isdrawn, mass 20 will produce a turning moment on arm 21, against theyieldable restraining action of spring 27, and cause the mass 20 and arm21 to seek the position represented by the broken-line outline of theseelements shown in Figure 3. The movement of mass 20 from the resting, orreference, position around the axis of shaft 22 will be proportional tothe amount of tilt of shaft 22.

It is important to the operability of the apparatus of the presentinvention that, when the central axis 14 is in a vertical position, thecenter of gravity of mass 20 should be spaced arcuately around axis 14with respect to the center of gravity CG of the mass 18. Accordingly,plate 19 is preferably secured to support member 13 by a plurality ofmeans, such as screws 28 threaded into support member 13 and passingthrough arcuate slots 29 provided in plate 19. By suitable initialplacement of plate 19 upon support member 13 and slight rotaryadjustment of plate 19 around axis 14 before tightening screws 28, thenormal resting position of mass 20 may be spaced arcuately around axis14 from center of gravity CG in the relative position represented inFigures 1, 2, and 3. In general, the normal resting position of thecenter of gravity of minor mass 20 should be spaced arcuately aroundaxis 14 from the center of gravity CG of major mass 18 by an amount lessthan 180 degrees and preferably not less than about 90 degrees.

In the drawing of Figures 1 and 3 the longitudinal axis of shaft 22 hasbeen represented as coaxial or coincident with the axis 14 of supportmember 13. It is to be noted, however, as will become apparent fromsubsequent description of the embodiment shown in Figures 8 and 9, thatthe axis of shaft 22 need not be coincident with axis 14 so long as thetwo axes are substantially parallel to each other. Stated broadly, thelever arm 21 should move in a plane which is substantially perpendicularto the axis 14, and the axis of shaft 22 should be substantiallyperpendicular to the plane in which lever arm 21 moves.

The apparatus of the present invention is readily adaptable to yieldinclination indications at a remote distance from the apparatus thus fardescribed. To this end there may be combined with the inclinationresponsive elements described above photoelectric means, similar to themeans disclosed by A. B. Hildebrandt in United States Patent 2,614,334issued October 21, 1952. Thus, the mass 20 may be provided with a planemirrored surface 20a and there may be aflixed to the upper surface ofplate 19 one or more plane mirrored surfaces 30. In the form ofapparatus shown in Figures 1 and 3, the respective planes of mirroredsurfaces 20a and 30 should be substantially horizontal when axis 14 isvertical.

Mounted within housing 10 upon a rotatable shaft 31 is a table member32. A bracket 33 carrying an electric lamp within a lamp shield 34 issecured upon table member 32 in a position such that light from the lampmay pass through a slit 35 in shield 34 and shine upon the mirroredsurfaces 20a and 30 when shaft 31 is rotated. Also secured to tablemember 32 is a bracket 36 carrying a photosensitive cell 37 in a fixedrelation to the light source 35. Photosensitive cell 37 is positionedrelative to light source 35 and mirrored surfaces 20a and 30 so thatduring some portion of each revolution of shaft 31 and table member 32said cell will receive light reflected from each of the mirroredsurfaces. As may be seen from Figure 1, the shaft 31 is preferablymounted coaxial with respect to the central axis 14. A plurality of sliprings 38 carried upon shaft 31 provide suitable sliding contacts forelectrical connections leading to and from the photosensitive cell 37and the source of light within light shield 34. Shaft 31 may be drivenat a uniform rate by a motor 39 mounted within housing 10. As will beapparent to workers in the art, motor 39 may be a clock-work motor or asmall electric motor and may include a gear reduction box (not shown)between motor 39 and shaft 31.

Referring now to Figures 5A and 5B there are shown, respectively, twographs such as would be produced by the apparatus of the presentinvention when employed with the elements shown and described inconjunction with Figure 5 of the aforementioned Hildebrandt Patent2,614,334. In the drawing of Figures 5A and 5B of the presentdisclosure, it is assumed that a single, relatively narrow, mirroredsurface 20a is arranged upon minor mass 20 and that two closely spacedmirrored surfaces 30 have been mounted upon plate 19 in the relationshown in plan view in Figure 3. It is further assumed that the lightsource 35 and photosensitive cell 37 scan these mirror surfaces in aclockwise direction. When the axis 14 of the apparatus is held in avertical position, passage of the light source and photosensitive cellover mirrored surfaces 30 produces the two kicks or responses 40 shownin Figure 5A. Passage of the light source and photosensitive cell overmirrored surface 20a in the course of revolution of table member 32produces the single kick 41. Since the rate of movement of the recordingchart and the rate of scanning of the mirrored surfaces are both heldconstant, the distance between kicks 40 and 41 are proportional to thearcuate spacing of mirrored surfaces 30 from mirrored surface 20a.Continued revolution of table member 32 causes the light source andphotosensitive cell to pass once again over the mirrored surfaces 30'and produces the kicks 42.

When the axis 14 of the apparatus is tilted away from vertical, the mass18 moves to a position such that its center of gravity is below thetilted axis, and this motion causes mirrored surfaces or indicants 30likewise to move. Under these conditions of tilt, the mass 20 carryingmirrored surface or indicant 20a moves arcuately toward mirroredsurfaces 30 by an amount proportional to the inclination of axis 14. Asshown in Figure 53, this action causes the kick 41a, produced byreflection of light from mirrored surface 20a, to move closer to thekicks 40a, produced by reflection of light from mirrored surfaces 30;and the distance between kicks 40a and kick 41a is proportional to theamount of tilt applied to axis 14. As will be apparent to workers in theart, the actual relation between the angle of tilt and the amount ofseparation between the recorded kicks 40a and 41a may readily bedetermined from a calibration chart provided for each inclinometer andrecorder assembly.

Turning now to Figures 6 and 7 there is shown a modifled embodiment ofthe apparatus of the present invention adapted for direct reading. Inthis embodiment, the housing 10 is provided with a flat base plate 43whose outer plane surface is perpendicular to the central axis 14. Theupper end of housing 10 may be closed by a transparent window 44 whichmay be held in place by appropriate internal and external rings 45 and46, respectively.

Secured within housing 10, by means such as set screws 12, is aconventional tapered roller bearing assembly 11a which may serve notonly as a swivel hearing but also as a thrust bearing. Secured centrallywithin the inner race element of the bearing assembly 11a is a lightweight support member 13 having a major pendulum mass 18 secured thereinwith the center of gravity of said mass eccentric with respect to theaxis 14. A restrained pendulnm or weighted arm assembly comprising theplate 19, minor pendulum mass 20, lever arm 21, pivot shaft 22, pivotbearings 23 and 24, pivot support brackets 25 and 26, and spiral hairspring 27 is mounted upon the upper end of support member 13. As in theembodiment illustrated and described in conjunction with Figure 1, theplate member 19 is preferably affixed to support member 33 by means ofscrews 28 which threadably engage support member 13. Arcuate slots,similar to the slots 29 shown in Figure 3, may be provided in plate 19although these slots are not visible in Figures 6 and 7. When theapparatus of Figures 6 and 7 is assembled, plate 19 may be mounted uponsupport member 13 and its position adjusted so that, when central axis14 is vertical, the center of gravity of mass is spaced arcuately aroundsaid axis a suitable amount relative to the center of gravity of mass18.

In the embodiment of apparatus shown in Figures 6 and 7, the outerextremity of lever arm 21 may be provided with a pointer 47, or othersuitable indicant, which may cooperate with a calibrated indicant scale48 carried upon a dial plate 49 which may be suitably afiixed to plate19 or support member 13. It will be apparent that lever arm 21 must bespaced slightly above dial plate 49 and also that the perimeter of dialplate 49 must not drag against the walls of housing 10. Indicant scale48 may be calibrated to indicate directly the degrees of inclination ofcentral axis 14.

Referring now to Figures 8 and 9 there is shown a preferred embodimentof apparatus in accordance with our invention, this embodiment ofapparatus being particularly adaptable to use as a well boreinclinometer. Besides the elements shown in the drawing, the housing 10may include suitable apparatus, such as a recording magnetic compass ora gyroscope for azimuthal orientation of the apparatus. Orientationapparatus of the above indicated type is well known in the prior art anddoes not form a direct part of the present invention. Accordingly, suchorientation apparatus will not be described herein.

Suitably aflixed within housing 10, substantially perpendicularly withrespect to the central longitudinal axis 14 thereof, is a mounting plate50. Arranged coaxially with respect to axis 14 and anchored'centrally inplate 50 as by means of transverse pin 51, is a vertical shaft 52depending below plate 50. Journaled upon shaft 52, as by upper and lowerprecision ball bearings 53 and 54, respectively, is a major pendulummass 18a. Mass 18a is so shaped that its effective center of gravity CGis eccentric with respect to shaft 52 and central axis 14, and it issupported for rotation on shaft 52 by ball thrust bearing 55 and a nut,or other retaining element, 56 fixedly engaging shaft 52.

Depending from and suitably aifixed to the lower end of mass 18a is acylindrical cup-like member 57 which functions, in part, as a supportmember analogous to the support member 13 shown in Figures 1 and 6. Thelower end of cup or support member 57 is closed by an inwardly depressedbottom portion 58 which thereby forms in the lower end of cup member 57an annular cavity 59. Rigidly afiixed to the lower end of shaft 52 as bymeans of nut 60 is an inverted cup 61 having the rim thereof concentricin the annular cavity 59. The cup-like support member 57 is partiallyfilled with a viscous liquid, such as a high viscosity-index lubricatingoil or other similar viscous liquid whose viscosity is not appreciablychanged by changes in temperature. It will be appreciated that theinverted cup 61 and the cup-like support member 57 cooperate, throughthe medium of the viscous liquid contained therein, to provide a viscousdrag capable of damping oscillatory movement of mass 18a around shaft 52and relative to housing 10.

So that the fluid contained Within cup 57 will not be readily spilledtherefrom, the upper end of cup 57 may be closed by a plate 62 having acentral opening adapted to pass shaft 52 as shown in the drawing. Askirt 63 depending from plate 62 around the periphery of the aforesaidopening may also be provided to prevent spillage of the fluid out of cup52.

Depending from the lower end of cup-like support member 57 is arestrained pendulum assembly, designated generally by the numeral 64. Ina preferred embodiment of our invention, the restrained pendulumassembly 64 is provided by suitable, and minor, modification of acommercially available direct current microampere panel-type electricmeter whose outer case is designated by the numeral 65. The electricalterminals 66a and 66b of the microammeter are secured to, andelectrically shortcircuited by, a circular metallic plate 67 having anupwardly projecting rim 68 adapted to embrace the lower end of cup-likesupport member 57. A plurality of set screws 69 penetrating transverselythrough the rim 68 provide means for securing the plate 67 to supportmember 57 and also provide means whereby the orientation of therestrained pendulum assembly 64 may be adjusted relative to the free, ormajor, pendulum mass 18a.

Contained within the microammeter case 65 is a permanent horseshoemagnet having the pole pieces 70a and 70b providing a suitable air-gaptherebetween. The aforesaid magnet is conventionally spaced from thewalls of case 65 and affixed relative thereto by means, such as screwsand spacers 71. Pivotally supported within the air gap of the magnet byupper and lower jewelled bearings 72 is a vertical shaft 73 carrying asmall coil of copper wire 74, the terminals of which are electricallyconnected in conventional manner (by means not shown) to terminal screws66a and 66b. The jewelled pivot bearings 72 are rigidly held in placerelative to the horseshoe magnet and other supporting structure bysuitable brackets 75. As may be seen from Figure 9, the pivot bearings72 need not be placed so that the shaft 73 is coaxial with respect tothe central axis 14. The axis of shaft 73 may, if desired, be eccentricwith respect to central longitudinal axis 14 but it is essential that,when the axis of shaft '73 is eccentric to axis 14, then the axis ofshaft 73 must be substantially parallel to axis 14.

Encircling the upper and lower ends of shaft 73 are,

'7 respectively, spiral hair springs 76:; and 76b. The inner ends "ofspiral springs 76a and 76b may be secured to shaft 73 while the outerends thereof are secured to support brackets '75. In a preferred form ofthe invention the Springs 7661 and 76b encircle the shaft 73 in oppositedirections, i. e. in a manner such that, when shaft 73 turns in a givendirection, it will tend to tighten the spiral 7 6d and simultaneouslyloosen the spiral 7 6b.

A'ffixed to the lower portion 7 of vertical shaft 73 is a horizontall'ever arm 77 Which may be the conventional indicator needle of themicroammeter mentioned herein'before. Adjacent the outer extremity ofthelevcr arm 77 there is secured thereon a minor mass 78. In thepreferred embodiment wherein restrained pendulum 64 comprises a directcurrent microarhmeter, the mass may consist of a small strip ofmirror-backed glass whieh is e'emented to the needle or arm 77. Thepurpose of the mirrored surface will be explained hereinafter.

It will be understood from consideration if the foregoing descriptionthat the tension of the two counterwound spiral springs 76a and 76b maybe adjusted relative to each other such that, when shaft 73 and centralaxis 14 are vertical, the arm 77 and minor mass 78 may be caused to takea normal resting position such as is represented by the full-lineoutline of these elements shown in Figure 9. The position of this normalresting position relative to the center of gravity of the mass 18a maythen be adjusted by loosening screws 69 and turning the entirerestrained pendulum assembly 64 relative to major mass 18a until minormass 78 is positioned arcuu ately around axis 14 relative to mass 18a asrepresented in Figure 9. It will be appreciated that, when the axis 14is tilted so that its upper end is above the center of gravity CG of themajor mass 18a, the arm 77 and the minor mass 78 will then move (againstthe restraining action of at least one of the spiral springs 76a or7612) toward the position represented in Figure 9 by the broken lineoutline of these arm and minor mass elements.

Attention is directed to the fact that the electrically short-circuitedcoil 74, positioned in the magnetic field existing between the permanentmagnet poles 70a and 70b, exerts a damping action (as distinguished froma constant restraining action) which minimizes oscillatory swing of theminor mass 78 around the axis of the shaft 73.- It will be apparent thatthe coil 74 may, if desired, be replaced by an equivalent small sheet ofnon-magnetic metal similarly mounted upon the shaft 73. According- 1y,the coil (or sheet of non-magnetic metal) 74 and the permanent magnethaving poles 70a and 7011 may be described as magnetic means operativelyassociated with the I lever arm 77 and the supporting member for damping's: cillation of the minor mass '78.

The face of the microamme'ter which constitutes a major portion of thestructure of restrained pendulum 64 is preferably covered by a sheet oftransparent material 79, such asglass or plastic. One or more narrowerstrips of mirror surfaced glass 80 may be cemented to the transparentmaterial 79 at a predetermined position thereon to provide a referenceposition indicant similar to the indicant referred to in connection withFigures 1 and 3'.

Positioned within housing 10 below the transparent face of restrainedpendulum assembly 64 is a source of light and a photosensitive cell 37which may be mounted for rotation in fixed relation around the centralaxis 14-. Since the structure, function, and operation of these elementsmay be identical with that already described in conjunction with Figures1 and 4, a repetition of that description here is not necessary.

It is to be understood that the specific forms of apparatus illustratedin the drawings are by way of example and that the invention is notrestricted thereto, but that obvious variations thereof may be made bypersons skilled in this particular art without departing from the scopeof the invention which is to be limited only by the following claims;

What we claim is:

1. An in'clino'rn'eter comprising, in combination: a support member;means mounting said support member for free rotation around the centrallongitudinal axis of said member; a major mass affixed to said supportmember with the center of gravity of said mass eccentric to said centrallongitudinal axis; a weighted arm assembly, said assembly comprising alever arm movable in a plane substantially perpendicular to said centrallongitudinal axis, pivot means mounting said le'ver arm upon saidsupport member for rotation of the lever arm around a second axis whichis substantially perpendicular to said lever arm plane, a minor massmounted upon said lever arm with the center of gravity of said minormass eccentric to said second axis, and resilient spring means anchoredat one end thereof to said support member and operatively connected atthe other end thereof to said lever arm to restrain rotary motion of thelever arm around said second axis; and means on said support member foradjusting the position of said weighted arm assembly so that the centerof gravity of said minor mass is spaced arcuately around said centrallongitudinal axis relative to the center of gravity 'of said major mass.

2. Apparatus in accordance with claim 1 in which said second axis iscoextensive with respect to said central longitudinal axis.

3. Apparatus in accordance with claim 1 in which said pivot meansincludes a shaft carrying said lever arm, and said resilient springmeans consists of a pair of spiral springs encircling said shaft inopposite directions, with the inner end of each spring affixed to saidshaft and the outer end of each spring anchored to said support memher.

4. An inclinometer comprising, in combination: a housing; an elongatedsupport member; means mounting said support member within said housingfor free rotation around the central longitudinal axis of said supportmember; a major mass afiixed to said support member with the center ofgravity of said mass eccentric to said longitudinal axis; a weighted armassembly, said assembly comprising a lever arm movable in a planesubstantially perpendicular to 'said longitudinal axis, pivot meansmounting said lever arm upon said support member for rotation of thelever arm around a second axis which is substantially perpendicular tosaid lever arm plane, a minor mass mounted upon said lever arm with thecenter of gravity of said minor mass eccentric to said second axis, andresilient spring means anchored at one end thereof to said supportmember and operatively connected at the other end thereof to said leverarm to yieldingly restrain rotary motion of said lever arm around saidsecond axis; and means on said support member for initially adjustingthe position of said weighted arm assembly so that the center of gravityof said minor mass is spaced arcuately around said central axis aselected amourif relative to the center of gravity of said major mass.

5. An incl'ino'rneter in accofc'l'ance with claim 4 having, incombination therewith: means operatively associated with said supportmember" and with said housing for damping oscillation of said major massaround said central longitudinal axis whenever said axis is tilted awayfrom vertical.

6. Ari inclihometer in accordance with claim 5 in which said means fordamping oscillationo f said major mass includes a viscous fluid, andwhich said weighted arm assembly includes magnetic means operativelyassociated with said lever arm and said support member for dampingoscillation of said minor mess around said second axis whenever thelast-mentioned axis is tilted away from vertical. ,7

7. An inclinometer in accordance with claim 4 and including: a firstindica'rit affixed to said' lever arm; a second indicant afiixed to saidsupport member at a selected reference position; and meaiiscarriedwi'thin said housing and operatively associated with said'indieants for producing outside said housing indications characteristicof movement of the first indicant relative to the second indicant.

8. An inclinometer in accordance with claim 7 in which both saidindicants are plane-mirrored surfaces arranged in planes which areperpendicular to said central longitudinal axis and said means forproducing an indication outside said housing includes a light sourceadapted to revolve around said central longitudinal axis, aphotosensitive cell adapted to revolve in fixed relation to said lightsource and so positioned as to receive reflected light from each of saidmirrored surfaces during some portion of each revolution around saidlongitudinal axis, and means for revolving said light source and saidphotosensitive cell around said axis at a uniform rate.

References Cited in the file of this patent UNITED STATES PATENTS

